EAGAN, Minn. -- The bye week allows Mike Zimmer to take an introspective look at his Minnesota Vikings defense and how far it has come from hitting rock bottom just over a month ago.

Since giving up 38 points to the Los Angeles Rams in Week 4, when Zimmer said he'd probably never had a unit that poor in pass coverage, the uptick for the Vikings' defense hasn’t stopped.

After yielding 381.5 yards and 27.5 points per game the first four weeks, the Vikings' defense experienced a considerable shift in Weeks 5 to 9, dropping those figures to 274.8 yards and 18.8 points per game.

Coming off a home win over the Detroit Lions -- with Matthew Stafford being sacked 10 times, a franchise record, including five times in the red zone -- Zimmer noted the momentum shift created by those stops inside the 20. He provided a look into what he felt led to the problems with his defense early on -- issues the Vikings appear to have moved past.

“Quite honestly, we’ve had to change up a lot,” Zimmer said. “For the last five weeks, probably, we’ve played pretty good defense. We were getting a lot of scheme things. Because we’re good at what we did, people are copying it. There’s a lot of teams now that are playing a style of defense similar to us. Now, all these offenses are attacking these defenses pretty much the same way. So, we’ve had to adjust and change coverages, and what we’ve done in the red zone, [Todd] Gurley beat us on the one route in the red zone, which was a scheme thing, basically. So, we’ve had to change up a lot of things that we’ve done. Luckily, our players have been able to execute it.”

In a copycat league, the ability to make adjustments is as important as ever. Zimmer estimated that about 10 or 12 teams have implemented the Vikings' base coverage as their own and said he has had "many" coaches tell him that they watch Minnesota’s blitz tape every week to see what they’re doing.

It’s nothing new for Zimmer, who has learned over his 24 years in the NFL that the only way to survive is by evolving.

“Quite honestly, I don’t think we’ve run hardly any Double A blitzes this year because everybody is practicing them, so we do something else,” Zimmer said.

That part is true. Over the past three seasons, the Vikings are using fewer Double A-gap blitzes, according to NFL Next Gen Stats, dropping from 19 in 2016 to just three blitzes in which two non-defensive linemen line up in the A-gap at the time of the snap and proceed to blitz the QB. Leaguewide usage, however, is down as well, a product of other coaches reacting to changes within their own scheme. Over the past three years, 31 other teams using Double A-gap blitzes have dropped from 1.0 to 0.6 percent (based on both players blitzing out of the Double A look).

Regardless, finding ways to make adjustments within the scheme -- whether it’s moving the line to a different spot or changing coverages depending upon the type of routes the offense is running -- has the Vikings rolling into the second half of their season on a high note.

"There’s a lot of smart people in this league, and in order to keep moving forward, you just can’t keep getting hit in the head with the same thing,” Vikings general manager Rick Spielman said of Zimmer. “A lot of the different adjustments he’s made, I think, has made a tremendous [impact] on how we’ve played over the last four or five weeks. Those are the adjustments that Zim made to the defense and to the scheme, which tells you, again, to me, that’s great coaching."

Several weeks ago, players spoke of the effect of those adjustments. A buzzword used to describe how Minnesota was able to get back to becoming the version of its No. 1 defense from 2017 was “simplify.”

“The offseason you have so much time to come up with all these great ideas, and I think sometimes it doesn’t go exactly how you drew it up,” linebacker Anthony Barr said in Week 7. “Going back to who you are, knowing your identity, doing what you do well has helped us be successful.”

Learning from the mistakes that caught up with them early on and diagnosing what went wrong was a critical part of the turnaround. Minnesota was tied for second in Weeks 1 to 4 with 10 plays allowed of 30 yards or more. Since Week 5, the Vikings have allowed only six of those plays, according to ESPN Stats and Information research.

Some of that has to do with how much better they’ve been able to defend play-action passes. As a whole, the defensive line’s ability to pressure the quarterback has been better in some weeks than others (the Vikings pressured Drew Brees a season-low 12.5 percent on his dropbacks, then escalated to pressuring Stafford on 37.5 percent of his dropbacks one week later), but it has stayed at a consistent rate throughout the first nine games (29.1 percent in Weeks 1 to 4 to 29.2 percent in Weeks 5 to 9).

Part of the improvement of the defensive line is the way the rotation of players among the front four has been able to affect the quarterback. It reached its peak in Week 9, when Tom Johnson and Stephen Weatherly added 2.5 and 1.0 sacks, respectively, to the monster day Danielle Hunter had with 3.5 sacks. Having Everson Griffen back in the mix after he was away from the team for five games also has provided a major boost.

Defending screens also has improved. Opponents are averaging about 2.5 yards per reception less on passes at or behind the line of scrimmage, according to ESPN Stats and Information data. The Vikings are closing fast; since week 5, they’re allowing just under 3 yards before first contact, or about 2 yards fewer than what they were allowing in Weeks 1 to 4.

“[Detroit] tried to run two of those rollout screens [on Sunday], and we got hurt with them earlier in the year. I think San Francisco had one and probably the Rams had one and there was someone else, so we’ve had to make adjustments on how we’re playing that,” Zimmer said.

The changes Minnesota have made since the end of September have the unit ranked sixth in total defense at the bye week. It took four up-and-down weeks at the start of the season for Zimmer to go back to the drawing board and adjust what the Vikings were doing that other teams had learned how to exploit. Doing that played no small role into why this team is 4-1 over its past five games.

“I sit there with Zim a lot watching, especially on Mondays, and going through everything and what’s happening and why it’s happening,” Spielman said. “It’s pretty incredible to see how they evolve things and why they evolve it.”